The long-term objectives of the proposed project are to determine whether and how intercellular communication (IC) mediated by gap junctions and cell adhesion molecules (CAM) is involved in multistage carcinogenesis, and to test the hypothesis that intact IC between tumor and surrounding normal cells can act as a tumor-suppressive element. The importance of heterologous IC (between (potentially) cancerous cells and surrounding normal cells) rather than homologous IC in carcinogenesis is stressed. The proposed project takes advantage of the fact that role of cell contact-mediated IC can be studied at the functional level as well as the gene and protein expression levels and that expression vectors for gap junction (connexin) and CAM genes are available. Dye-transfer assay to measure gap junctional IC (GJIC) in tissue slices from animals and surgically removed human samples is available. Emphasis is given to studying the role of IC in carcinogenesis in vivo (including in human tissues) and to exploring molecular mechanisms of regulation of IC during carcinogenesis. Specific aims and experimental designs are: (i) To determine the involvement of changes in IC during animal carcinogenesis and the effect of tumor-promoting agents in vivo, employing multistage rat liver and mouse skin models. (ii) To study alterations of IC during human carcinogenesis employing normal/transformed pairs of cultured human cells, and surgically removed human liver and esophagus tumor tissue samples. (iii) To examine the relationship between GJIC and tumor suppression. It is planned to (a) transfect expression vectors of connexin and/or CAM genes into tumorigenic human cell lines and look for suppression of tumorigenicity, (b) measure GJIC of human tumorigenic cells before and after tumor suppression by transfer of normal chromosomes, and (c) study possible mutations of connexin and CAM genes in human tumors. (iv) To explore molecular mechanisms involved in control of GJIC (a) by tumor-promoting agents and (b) by cell-cell recognition molecules. Phorbol ester-mediated control of connexin mRNA or protein expression/function will be studied in connection with possible involvement of protein kinase C, using mouse epidermal cells expressing a transfected CAM gene. (v) To test whether cellular oncogene expression is controlled by GJIC and whether its modulation is involved in cell transformation. It is proposed to use BALB/c 3T3 cells since a relationship between chemically induced mutation of a specific cellular oncogene and its involvement in transformation has been recently established.